Secondary harmonic generator having waveguides for a laser beam

Abstract

An optical wavelength conversion device, which is provided with a rigid type waveguide for efficiently converting a fundamental wave into the secondary harmonic wave and emitting the latter in the form of a beam of a circular or elliptic shape in section, and a process for manufacturing the ridge type waveguide. The optical wavelength conversion deivce essentially includes: an optical waveguide formed on a substrate of a nonlinear optical material so as to generate a secondary harmonic wave by Cerenkov radiation, and which has a first waveguide passage for confining a fundamental wave and converting it into the secondary harmonic wave, and a second waveguide passage for confining the generated secondary harmonic wave and propagating it toward an end face for emission therefrom.

I claim as my invention: 
     
       1. An optical wavelength conversion device, comprising: an optical waveguide formed on a substrate of a nonlinear optical material so as to generate a secondary harmonic wave by Cerenkov radiation, and having a first waveguide passage for confining a fundamental wave and converting it into a secondary harmonic wave, and a second waveguide passage for confining said secondary harmonic wave and propagating it toward an end face for emission therefrom, wherein said first and second waveguide formed with a ridge shape on a substrate, and said first waveguide passage is formed so as to be in contact with said second waveguide passage on at least one of the lateral side surfaces of said ridge which is perpendicular to the major surface of said substrate, wherein the following condition is satisfied,   n.sub.2 >n.sub.3 >n.sub.1     wherein n 1 , n 2  and n 3  are, respectively, the refractive indices of said substrate, said first waveguide passage and said second waveguide passages, and wherein said first and second waveguide passages are formed so as to satisfy the conditions     W.sub.r f<a<W.sub.r s,       W.sub.r f or W.sub.r s<b, and       W.sub.r s<c     wherein a is the width of said first waveguide passage in a direction which is parallel with said major surface of said substrate, b is the depth of said first waveguide passage in a direction which is perpendicular to the major surface of said substrate, c is the depth of said second waveguide passage in a direction which is perpendicular to the major surface of said substrate, W r  F is the cutoff thickness for the fundamental optical wave, and W r  s is the cutoff thickness for the secondary harmonic wave.   
     
     
       2. A process for manufacturing a ridge type optical waveguide device comprising the steps of: forming, on a substrate of a nonlinear optical material which has a refractive index n 1 , an optical waveguide layer which is to be used as a second waveguide passage and which has a refractive index n 3  (n 3  >n 1 ) by diffusion of titanium;   forming a metal layer on said substrate;   selectively forming a photoresist layer on said metal layer;   selectively removing a part of said metal layer and said optical waveguide layer, using said photoresist layer as a mask;   forming, on a lateral side of said optical waveguide layer, a proton exchange layer which is to be used as a second waveguide passage and which has a refractive index n 2   (n 2  >n 3  >n 1 ), by a heat treatment in an aqueous solution capable of proton exchange with optical waveguide portions which are exposed by removal of said metal layer; and   removing the remaining portions of said metal layer.   
     
     
       3. A process as defined in claim 2, comprising, after formation of said proton exchange layer, the step of etching said proton exchange layer into a thin layer by reactive ion etching using selectively unremoved portions of said metal layer as a mask.